A crowning achievement of advanced intelligence involves the ability to use objects as tools. Even before children become sophisticated users of the tools of our culture they use objects to act toward target outcomes or desired goals. This proposal investigates infants'developing ability to use tools to retrieve desired objects, and to recognize the goal-directed nature of others'tool use actions. Specifically, I assess the impact of active and observational experience on infants'ability to learn how to use tools, to understand the tool use actions of others and to generalize their knowledge to novel tool use contexts. Across several studies, infants receive active training and practice using a tool to retrieve out-of-reach objects or watch another person use the tool successfully to obtain out-of-reach objects. Infants subsequently take part in generalization trials designed to assess infants'ability to generalize tool use strategies to novel tool use contexts in their own actions and/or a violation-of- expectancy paradigm that assesses infants'ability to anticipate the goal of another person's tool use actions. Based on previous and preliminary work it is predicted that active experience will play a privileged role in infants'ability to learn how to use tools, and to extend their tool use knowledge to the actions of others. The findings from this work will provide important information regarding the development of tool use representations, infants'understanding of agency and causality, and mechanisms supporting early learning. In addition, these results may be particularly relevant to the diagnosis and remediation of autism, a developmental disorder that is characterized by deficits in reasoning about other people's behavior. RELEVANCE: The proposed research seeks to investigate early learning mechanisms by assessing the role of observational and active experience in infants'tool use behavior and their understanding of others'tool use acts. This work will provide important information regarding the factors and processes involved in typical cognitive and social development, information that can then be used in the diagnosis and remediation of developmental disorders, such as autism.